The objective of this project is to define more precisely the organization of the respiratory controller so that the role of the carotid body particularly can be more precisely defined, and the effects of exercise and depressant drugs on respiration better understood. This research will utilize computer modeling techniques to simulate the physiologic system so that systems analysis may be employed to define the optimal forcing function for estimating parameters within the system. The forcing function will be chosen not merely to suit the convenience of the experimenter, but to estimate a parameter of the physiologic system with minimal variance. A new novel technique has been devised so that the end-expiratory carbon dioxide and/or oxygen waveform can be computer controlled to achieve any desired waveform. Exercise workload and cueing of breathing can also be computer controlled to similarly generate various forcing functions. In addition, techniques have been evolved so that with repetitive averaging, the noise (breath-to-breath variation) in the output signal of the respiratory system can be minimized. This is essential to precisely define system parameters. This added insight to the function and organization of the respiratory controller will be of value in treating patients with diseases that affect respiration, as well as in evaluating a new maneuver that might be used in persons acclimating to different atmospheres.